Muscle press juice

In the field of food science, knowledge about disintegration of cell membranes is important if deterioration of meat quality by freezing and freeze-storage is to be more fully understood (3). The presence of membrane-bound enzymes in the muscle-press juice after freezing and thawing could lead to a method for differentiating between nonfrozen meat and frozen and thawed meat. 

Figure I. Influence of storage (+4°C) on the activity of glutamic dehydrogenase in muscle press juice from bovine longissimus dorsi (time...

Percent of total GOT activity in the muscle press juice. 

Frozen storage of muscle tissue for three months at — 20°C does not cause an additional increase in enzyme activities in the muscle-press juice obtained after thawing (10), except for GOTM (9). However, it is possible that a further release of mitochondrial enzymes does occur along with a compensating inactivation of enzymes. 

Figure 4. Influence of freezing (—20°C) and freeze-dehydration of prerigor muscle tissue on the activities of aconitase and fumarase in the muscle press juice. Percent of the total extractable activity. The press juice was prepared from the thawed tissue and the rehydrated tissue...

Figure 5. Influence of freezing (—20°C) and thawing of poultry thigh muscles (postrigor) on the GOTM activity in the muscle press juice. (Ordinate) GOTm activity as a percent of the total GOT activity in the press...

The release of enzymes from mitochondria by treatment of the tissue was determined by pressing juice from a small piece of muscle and analyzing this juice for enzyme activity. The activity of a given enzyme was then expressed as a percent of the total activity of that enzyme existing in the supernatant fluid of a muscle homogenate prepared using phosphate buffer-Triton X-100 (6,8). Most of die experiments were carried out with white and red muscles of pigs and cattle. The activities of the different enzymes were determined as described by other authors... 

Table I. Enzyme Activities in the Press Juice of Prerigor Bovine Longissimus Muscle before and after Freezing6 (10)...

Figure 2. Results from low voltage electrophoresis of the press juice from nonfrozen and frozen-thawed porcine muscle. Psoas muscle, excised 5 days postmortem and frozen at —20°C for 20 days. (Ordinate) GOT...

This procedure also can be used to differentiate between fresh and frozen-thawed fish. In fresh, homogenized carp muscle we found four GOT isozymes—one sarcoplasmic and three mitochondrial (48). Upon freezing of whole carp, the mitochondrial isozymes (GOTmi, GOTM2, GOTM3) are released (Table VII) (49). Thus, press juice from fresh carp muscle exhibits one band, whereas after freezing and thawing four bands appear. 

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